Add function to check is sector blank.

Note:

NuttShell (NSH)
nsh> eeprom test
-------------------------------------------------------------------------------
RM0090 Table 5. Flash module organization (STM32F40x and STM32F41x)
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[DEBUG]Check_Sector_Erased :SS = 0x08000000, SE = 0x08003FFF, SIZE = 0x00000001
[DEBUG]internal_flash_test :Check_Sector_Erased 0  (DATA)
-------------------------------------------------------------------------------
[DEBUG]Check_Sector_Erased :SS = 0x08004000, SE = 0x08007FFF, SIZE = 0x00004000
[DEBUG]internal_flash_test :Check_Sector_Erased 1  (ERASED)
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[DEBUG]Check_Sector_Erased :SS = 0x08008000, SE = 0x0800BFFF, SIZE = 0x00004000
[DEBUG]internal_flash_test :Check_Sector_Erased 2  (ERASED)
-------------------------------------------------------------------------------
[DEBUG]Check_Sector_Erased :SS = 0x0800C000, SE = 0x0800FFFF, SIZE = 0x00004000
[DEBUG]internal_flash_test :Check_Sector_Erased 3  (ERASED)
-------------------------------------------------------------------------------
[DEBUG]Check_Sector_Erased :SS = 0x08010000, SE = 0x0801FFFF, SIZE = 0x00000001
[DEBUG]internal_flash_test :Check_Sector_Erased 4  (DATA)
-------------------------------------------------------------------------------
[DEBUG]Check_Sector_Erased :SS = 0x08020000, SE = 0x0803FFFF, SIZE = 0x00000001
[DEBUG]internal_flash_test :Check_Sector_Erased 5  (DATA)
-------------------------------------------------------------------------------
[DEBUG]Check_Sector_Erased :SS = 0x08040000, SE = 0x0805FFFF, SIZE = 0x00000001
[DEBUG]internal_flash_test :Check_Sector_Erased 6  (DATA)
-------------------------------------------------------------------------------
[DEBUG]Check_Sector_Erased :SS = 0x08060000, SE = 0x0807FFFF, SIZE = 0x00000001
[DEBUG]internal_flash_test :Check_Sector_Erased 7  (DATA)
-------------------------------------------------------------------------------
[DEBUG]Check_Sector_Erased :SS = 0x08080000, SE = 0x0809FFFF, SIZE = 0x00000001
[DEBUG]internal_flash_test :Check_Sector_Erased 8  (DATA)
-------------------------------------------------------------------------------
[DEBUG]Check_Sector_Erased :SS = 0x080A0000, SE = 0x080BFFFF, SIZE = 0x00000001
[DEBUG]internal_flash_test :Check_Sector_Erased 9  (DATA)
-------------------------------------------------------------------------------
[DEBUG]Check_Sector_Erased :SS = 0x080C0000, SE = 0x080DFFFF, SIZE = 0x00000001
[DEBUG]internal_flash_test :Check_Sector_Erased 10 (DATA)
-------------------------------------------------------------------------------
[DEBUG]Check_Sector_Erased :SS = 0x080E0000, SE = 0x080FFFFF, SIZE = 0x00000001
[DEBUG]internal_flash_test :Check_Sector_Erased 11 (DATA)
-------------------------------------------------------------------------------

Signed-off-by: cctsao1008 <chiacheng.tsao@gmail.com>